The primary goal of the protocol is to provide comparative data on the cardiovascular and central nervous systems, in order to assess analgesia during a general anesthetic. Continuous monitoring of heart rate, systolic, diastolic and mean blood pressure is done during the anesthesia, as indirect indices of autonomic nervous system activity. Periodic somatosensory evoked potentials after standard stimulation are collected, because they are preserved, even at deep levels of general anesthesia, and because certain components are modified by analgesics and by narcotic antagonists. Brain cortical activity is also assessed by EEG power spectral analysis. Data are collected, processed and stored on line by a mobile Digital MINC-11 computer. Changes, particularily in electrical reactivity of the brain are being compared, when different anesthetic techniques are used: when no narcotic is used, when small doses of narcotics are used and when large doses of narcotics are employed.